Intra-abdominal dermatophytic pseudomycetoma in a Persian cat.

Mycetoma is an infectious, noncontagious disease caused by free-living bacteria (actinomycetoma) or fungi (eumycetoma) that are traumatically implanted into the body.1 In humans, the hand and foot are the most commonly affected sites and involvement of the abdominal wall or viscera is rare.1–3 Causal agents of mycetoma produce organized aggregates of bacteria or fungal hyphae called grains in affected tissue.1 Clinically, the 3 distinguishing features of mycetoma are formation of nodular inflammatory lesions with secondary fibrosis, formation of fistulae that may penetrate deep tissue, and the presence of bacterial or fungal grains in the affected tissue and exudate.4 The initial lesion of mycetoma is typically a painless scratch or small papule.4 Because little discomfort is associated with early lesions, mycetomas are usually insidious, and patients generally present late with advanced disease.1 As the disease progresses, affected tissue is replaced by a tumorous mass of chronic inflammation and fibrosis that may clinically resemble neoplasia.1 Dermatophytes may rarely invade deep cutaneous tissue to produce mycetomalike, nodular or dispersed, suppurative and granulomatous, inflammation of the dermis and subcutis.5 The dermatophytes within these lesions may aggregate into clusters that resemble the tissue grains of eumycetoma. These clusters of dermatophytes are not considered to be true grains because individual fungal elements may often be found in the tissue as well.1 Therefore, some prefer the term pseudomycetoma to distinguish the dermatophytic lesions from those of other fungal mycetomas.1,5,6 In humans, pseudomycetoma has been caused by species of the genera Microsporum (M canis, M audouinii, and M ferrugineum) and Trichophyton (T mentagrophytes, T rubrum, T tonsurans, and T violaceum).5 Systemic dermatophytosis is extremely rare and resembles other deep infections caused by fungi such as Aspergillus sp.5 Definitive identification of the causal agent of mycetoma or pseudomycetoma is best done through characterization of the organism in culture.1 Immunohistochemical identification of fungi, including dermatophyte species, is possible but not widely available.7–9